// FINISHING — CHEM FILM / CONVERSION COATING
Chemical Conversion Coating (Chem Film)
Alodine / chromate conversion coating for aluminum — corrosion passivation, electrical conductivity retention, and paint adhesion in clear or gold, to MIL-DTL-5541.
Chemical conversion coating — commonly called chem film, Alodine, or chromate — reacts with the aluminum surface to form a thin, corrosion-resistant layer that preserves the metal’s electrical conductivity. Unlike anodizing, the coating adds essentially no measurable thickness, making it ideal for close-tolerance parts and assemblies that must remain electrically conductive across mating surfaces. Rigid Concepts coordinates chem film through our trusted finishing partner NorTex Metal Finishing.
What chem film does
The conversion coating reacts chemically with the aluminum oxide to form a chromate compound that passivates the surface against further oxidation. The result is a thin, continuous film that resists corrosion, provides an excellent bonding surface for paint and primer, and — unlike anodize — does not insulate the part electrically. This makes chem film the standard choice for avionics panels, RF enclosures, grounding plates, and any aluminum assembly where both corrosion protection and low contact resistance are required.
- Corrosion passivation of aluminum surfaces
- Electrical conductivity preserved (unlike anodize)
- Superior paint and primer adhesion base
- Negligible dimensional buildup — safe on tight-tolerance features
- Clear (Class 1A) and yellow/gold (Class 3) available
Clear vs. yellow/gold
Class 1A (clear) chem film is the standard for parts that will be painted or bonded — it provides full corrosion protection and adhesion without adding visible color. Class 3 (yellow/gold) uses a heavier chromate film offering slightly higher corrosion resistance in the bare condition and is commonly specified for aerospace and defense parts that must be visually distinguishable from untreated aluminum.
Material and size capability
Chemical conversion coating is an aluminum process. Our partner NorTex handles parts up to 45" × 20". Larger assemblies can be discussed — contact us with your drawing.
| Process | Alodine / chromate conversion coating |
|---|---|
| Colors / classes | Clear (Class 1A) · Yellow/gold (Class 3) |
| Max part size | 45" × 20" |
| Substrate | Aluminum alloys |
| Dimensional impact | Negligible — no significant buildup |
| Standard | MIL-DTL-5541 |
For aluminum parts that need a harder, more wear-resistant surface rather than conductivity, see Type II & III anodizing. Chem film is commonly specified alongside our aluminum CNC machining for aerospace, defense, and electronics enclosures where conductivity matters.
// FAQ
Frequently asked questions
Both processes treat aluminum surfaces, but they produce very different results. Anodizing grows a thick oxide layer that is electrically insulating. Chem film forms a thin chromate conversion layer that is electrically conductive, adds virtually no thickness, and is often used as a paint primer. Choose chem film when conductivity or minimal dimensional change is required; choose anodize when hardness, wear resistance, or color are the priority.
Yes — bare chem film provides meaningful corrosion resistance, particularly the heavier Class 3 (yellow/gold) film. For long-term outdoor or salt-spray exposure, a topcoat of paint or primer over the chem film is the standard approach and provides excellent combined protection.
MIL-DTL-5541, the military specification for chemical conversion coatings on aluminum and aluminum alloys. Class 1A (clear) and Class 3 (yellow/gold) are both available.
Yes. Chem film works on wrought and cast aluminum alloys. The surface finish and alloy chemistry affect the result slightly, so let us review your drawing if the alloy is non-standard.
Send us the hard one.
Upload your drawing or STEP file and we'll come back with pricing and lead time — from a single high-mix part to full production runs, held to exacting tolerances.